Selection of epoxy resin for insulating powder coating for electromagnetic wire

Since the beginning of the 21st century, powder coatings have become the mainstream of today's green coatings with their environmentally friendly, clean, zero VOC release, easy assembly line operation, high efficiency, high performance and so on. Powder coatings occupy an increasingly important position in the insulation materials for electronics and motors. The products are widely used in various fields such as motors, electronics, high voltage electrical appliances, automotive industry, and aerospace machinery. However, the insulating powder coating is still in its infancy in the field of electromagnetic wire coating. The performance of the product is not much, and the overall performance is very different from that of the solvent-based coating represented by polyimide. This restricts the insulation to a large extent. The marketing and application of powder coatings in this field.

This paper mainly studies the insulating powder coatings for electromagnetic wire (aluminum wire) coating currently applied in the field of motors, and obtains pure epoxy-based insulating powder coating products. The softening breakdown temperature can reach above 150 °C, and the solvent type can be realized. Partial replacement for insulating coatings.

It is well known that pure epoxy powder coatings have excellent insulation and corrosion resistance, which is closely related to the molecular chain structure of epoxy resins. The hydroxyl group in the epoxy resin is highly polar, and can form a chemical bond with the metal surface, so that the adhesion of the resin is particularly good; the ether bond in the molecular structure provides excellent chemical resistance and corrosion resistance, and the bending property is also good; propane The base and the benzene nucleus impart heat resistance and mechanical rigidity to the epoxy resin; wherein the epoxy group and the hydroxyl group have reactivity, and react with a specific compound to crosslink into a network structure.

At present, the epoxy resins for powder coatings commonly used in the market mainly include bisphenol A type and o-cresol type, and bisphenol A type epoxy resin, especially E-12 type bisphenol A type epoxy resin in powder coating. The field is more widely used and has excellent comprehensive performance. However, the epoxy functional groups in the molecular chain of bisphenol A type epoxy resin are generally two, and the crosslinking density formed after crosslinking reaction with the curing agent is limited, and the o-cresol novolac type ring is limited. The oxyresin may have a plurality of epoxy functional groups, and a large crosslink density may be formed after participating in the reaction, thereby improving the heat resistance of the coating film, but at the same time impairing the toughness of the coating to some extent. The insulating powder coating for electromagnetic wire is different from the powder coating for motor stator and rotor. It requires the coating film to have excellent flexibility properties while having insulation properties (electrical properties and thermal properties).

A bisphenol A epoxy resin having an epoxy equivalent of 700 to 900, an o-cresol novolac epoxy resin having an epoxy equivalent of 200 to 300, and an o-cresol novolac epoxy having an epoxy equivalent of 800 to 900 were used in the test. Resin B, micronized dicyandiamide as curing agent, 2-methyl-imidazole (2MI) as curing accelerator, general-purpose leveling agent, benzoin and deaerator and pigment, no filler, contrasting different rings The effect of the type of oxygen resin on the properties of the film.

Effect of epoxy resin type on the performance of powder coatings

The o-cresol novolac epoxy resin A is too rigid and has poor compatibility with the bisphenol A epoxy resin, although it can greatly improve the heat resistance (softening breakdown temperature) of the coating, but also It seriously damages the flexibility of the coating and therefore should not be used as an insulating powder coating formulation with high toughness requirements such as magnet wires.

Epoxy Resin B is a trifunctional phenolic epoxy resin. Its rigidity is relatively small compared to Epoxy A, but the toughness is increased. As the amount of addition is reduced, the coating toughness is increased and softening is applied. The wear temperature is lowered, and the ratio of bisphenol A epoxy resin 150 (bisphenol A type) / 50 can meet the toughness requirements of the coating film, and the softening breakdown temperature rises to 142 ° C. Therefore, in this study, it was decided to use a bisphenol A type epoxy resin E-12 in combination with o-cresol novolac epoxy resin B (E-12/epoxy resin B=150/50) as a resin system for the formulation.